1. Field of the Invention
The present invention relates to a test device for measuring the concentration of an analyte in a fluid sample, notably to a test device for analysing blood glucose or other analytes in bodily fluids.
2. Description of the Prior Art
Diabetics regularly need to test samples of their blood to determine the level of blood glucose. The results of such tests may be used to determine levels of medication needed to treat the diabetes at the time. In one known type of system, disposable sensors are used to test the blood. The sensors typically take the form of test strips which are provided with a reagent material that will react with blood glucose to produce an electrical signal. Conductive tracks on the test strip relay the electrical signal to a meter which displays the result. After a sample of blood has been applied to the test strip and the measurement has been taken, the test strip is disposed of. In order to couple the conductive tracks on a test strip with the meter, the test strip needs to be inserted into a sensor holder prior to the start of testing. The sensor holder has corresponding electrodes which are brought into electrical contact with the conductive tracks of the test strip. Test devices are known in which a plurality of test strip are provided on a cartridge disc. Each strip is housed in its own sensor slot, and means are provided to eject a test strip from its slot when required, and to automatically locate it in a sensor holder. Examples of test devices with test strip dispensers are described in U.S. Pat. No. 5,660,791, European Patent Application No. 0 732 590, and European Patent Application No. 0 738 666.
A problem with test strips is that they have only a limited shelf life, and exposure of test strips to the atmosphere reduces the shelf life further. Test strips open to the atmosphere will typically have a shelf life of about two to three months, whereas test strips which are sealed from the atmosphere will have a shelf life of about six to 12 months.
It has been proposed in WO 94/10558 to provide a stack of disposable test elements in a cylindrical housing, the stack being urged towards a test station to form a liquid-proof seal. In DE 196 39 226 A1 it is proposed to provide a test device with a cartridge that may have a plurality of chambers containing test strips, each of which chambers may be individually sealed to preserve the shelf life of the strips therein. A user removes the seal for each chamber when required, and a timing circuit may be activated either by the user or when the cartridge is pushed into the device. After a set time period has elapsed, an alarm or other indication reminds the user that the time period for using the strips has elapsed.
It is an object of the present invention to provide an improved test device.
According to an aspect of the present invention there is provided a test device for testing of analyte concentration in a fluid to be applied thereto, the device comprising:
a) a plurality of sensors arranged in a stack, each of said sensors carrying reagent means for producing an electrical signal in response to the concentration of analyte in an applied fluid, each of said sensors having a plurality of electrode tracks for transmitting said electrical signal;
b) a housing having an opening therein and containing the said stack of sensors;
c) electrical contacts mounted in relation to the housing for engaging with electrode tracks on a sensor at an engagement location;
c) a meter connected to the said electrical contacts, having electronics means for producing a signal output which is dependent on the electrical signal from a sensor when the sensor is engaged with the said contacts;
d) a transport member rotatably mounted in the opening of the housing, having an axis of rotation which spans the opening and having an outer surface which is provided with a recessed region adapted to receive a single sensor from the stack;
e) spring means within the housing which urge the stack of sensors towards the transport member and which urge a single sensor into the said recess when the recess is suitably aligned adjacent to the stack;
f) sealing means for making a moisture tight seal between the transport member and the stack when the transport member is in a specified rotational position; and
g) wherein rotation of the transport member with a sensor in the recessed region will transport the sensor to the engagement location or to a position where the sensor can be moved to the engagement location, whereby electrode tracks of the sensor can engage with the said electrical contacts.
With the transport member in a start or home position, the sealing means keeps moisture from sensors in the stack when the device is not being used. The device may be factory assembled under controlled temperature and humidity conditions, and kept sealed until a user is ready to use a sensor. In a preferred embodiment the sealing means also provide a moisture-proof seal when the sensor is in the engagement location, so that sensors in the stack are protected while an analyte measurement is being taken.
The invention will be described with reference to the testing of glucose concentrations in blood, but it will be understood that the invention is not limited to this embodiment and is of general applicability for testing analytes in bodily and other fluids.
The transport member may take the sensor to the engagement location by rotational motion alone. Additional pushing means may be provided to translate the test strip to the engagement location. Such pushing means may be provided by a captured pusher which engages with a track on the housing so as to move the test strip during rotation of the transport member. Alternatively, separately actuatable pushing means could be provided to push the sensor to the engagement location after rotation of the transport member to a suitable position. It will also be understood that other means could be provided for moving the test strip after it has been carried by the transport member, for example rotation or a combination of rotation and translation.
The electrical contacts may be brought automatically into contact with electrode tracks on the sensor in the engagement location, for example by means of spring biasing. Alternatively, the user could move the electrical contacts to achieve the necessary contact at the engagement location.
After a measurement has been taken, it would be possible to remove the used sensor from the engagement location by manual intervention from the user. However, to avoid the need for handling of the used sensor it is preferred that the transport member can be further rotated from the engagement location to an exit location at which the sensor can fall out or be pushed out by ejection means.
After completion of a test measurement, and ejection of the used sensor, the transport member is returned or advanced to the start position. This may be done manually by the user or by means of a motor. The transport member is preferably urged by a return spring to return to the start position.
For simplicity the transport member is preferably circular in cross section, for example a cylindrical feed barrel. However the transport member could have a sectional shape that is not circular, for example oval, square or triangular.
The sealing means may be provided on an external surface of the transport member, or separate sealing means may be provided that make a seal between the transport member and the housing or the stack of sensors. Where the seal is made with the housing, the opening in which the transport member is mounted must of course be the only opening to the inside of the housing. In a preferred embodiment the sealing means comprises a retractable shroud which surrounds the stack of sensors and which sealingly engages with the transport member when in an extended configuration. In another preferred embodiment, the sealing means is provided by a seal on a door which opens and closes the opening according to the rotational position of the transport member. The door may be provided with one or more teeth to restrain movement of the stack, and the transport member may be provided with one or more blades to take over the restraining function from the teeth when the door is open, prior to the recessed region of the transport member being brought into register with the stack. This embodiment has the advantage that the door may remain closed, and the seal intact, at all times except for the brief period when a sensor is being loaded and taken to the engagement location. The sealing means may be formed from any suitable material, for example natural or synthetic rubber.
The sensors may be conventional test strips of known construction. The invention will for convenience be described hereinafter with reference to test strips; however it is to be understood that other shapes of sensor could also be employed, for example square sensors or discs.
The invention provides a test device in which test strips are dispensed via a rotationally mounted transport member so that each test strip is conveniently brought to a location where it can engage with meter contacts and where it can receive a drop of fluid. Accordingly, another aspect of the invention provides a test device for testing of analyte concentration in a fluid to be applied thereto, comprising: a housing containing a stack of test strips and having an opening therein; a transport member rotatably mounted in the opening of the housing, having an axis of rotation which spans the opening; the transport member having a recessed region adapted to receive a single test strip; and spring means which urge the stack towards the transport member; wherein rotation of the transport member with a test strip in the recessed region thereof will bring the said test strip to an engagement location at which it can be engaged with electrical contacts of a meter and at which the test strip will be accessible to permit a user to apply a drop of fluid thereto.
In a preferred embodiment, each test strip comprises a base member having a working area to which the fluid is to be applied, containing the reagent means, and a non-working area adjacent to the working area, wherein the total thickness of the test member in at least a portion of the non-working area is at least as great as the total thickness of the test member in the working area.
By making the non-working area at least as thick as the working area, scuffing or abrasion of the working area in a stack can be reduced. Moreover, if a compressive load is applied to a stack of the test members, this may be spread out over a greater area, thereby reducing the possibility of compressive damage to the working area.
In a preferred embodiment, at least a part of the non-working area is of greater total thickness than the thickness of the working area. This further reduces the likelihood of damage to the working area by scuffing or abrasion when in a stack. The difference in thickness is preferably from 1 to 20 xcexcm, notably from 5 to 10 xcexcm.
To build up the working area, a plurality of layers are sequentially applied to the base layer, for example by screen printing, typically with curing or drying steps between the application steps. The layers which are printed typically comprise electrode patterns, a reagent layer, and a mesh layer (for spreading out an applied fluid). As a result of the application of these layers, the working area of a conventional electrochemical test strip is typically about 100 xcexcm thicker than the non-working area, which contains the electrode tracks and, typically, a dielectric layer. A stack of 100 test strips will therefore be about 10 mm thicker in the working area than in the non-working area. In a test strip in accordance with the present invention, at least a part of the non-working area may be made thicker by any suitable means. Suitable means include, for example: a printed relief ink; an applied pad or tape; embossing of the base layer or an intermediate layer; or an extension of the mesh layer from the working area.
Further objects and advantages of the invention will be apparent as the description proceeds.
The term xe2x80x9cspring meansxe2x80x9d is used herein for convenience. It will be understood that this term includes conventional springs and other biasing or urging means which perform an equivalent function; for example elastic or pneumatic biasing means.